Many different liquids, including liquefied gases such as LPG and LNG, are stored in tanks of various types. The chemical and physical properties of a number of such liquids makes them hazardous, especially those which are highly flammable. Because of the inherent danger which many liquids pose if they leak or escape from a primary storage tank or vessel, especially in relatively populated areas, it has been required to surround the tank or vessel with an outwardly positioned containment wall or barrier of sufficient size and quality so as to encompass a space or volume adequate to capture and hold most or all of the liquid content which the storage tank is capable of storing. Since there may be no or little warning if the storage tank fails, it is generally considered desirable for all escaping liquid to be captured initially by the containment wall and held in a containment space until an appropriate decision can be made as to the disposition of the liquid. If it is decided to remove the liquid for restorage or disposal a means for draining the liquid from the containment is needed. However, any drain pipe or conduit should generally be remotely operable because of the properties of many of the liquids and it should not permit the liquid to enter it until the liquid is to be drained from the containment space.